We present here an exploration of the relationship among post-roll bonding process variables, interfacial and overall mechanical properties of a 3-ply STS-Al-Mg laminated composite. The effect of post-annealing conditions upon the evolution of interface microstructure is first analyzed by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) attached with energy dispersive spectroscopy (EDS). Taking the composition and thickness of each intermetallic compound layer into account, results devoted to the interfacial microstructure and overall mechanical properties are also given. Local mechanical properties for the generated diffusion layers were first determined by nanoindentation tests. The mechanism of improvement of interfacial bonding is then verified by means of uniaxial tensile and bending tests. Finally the competitions between two contradictory effects, viz., interface strengthening by the generation of IMCs and the corresponding loose of overall ductility due to the embrittlement, is discussed.